San Andres Formation, Permian geological formation in Arizona and New Mexico, United States.
The San Andres Formation spreads across the southwestern United States and consists of alternating layers of limestone and dolostone. These rock sequences contain structures and sediment patterns that reveal how ancient shallow seas once covered this region.
This formation originated during the Permian period roughly 250 million years ago when shallow seas covered the southwestern landscape. Its layers accumulated from sediment deposits in these ancient marine environments.
Native American communities have long-standing connections to lands where this formation appears. They incorporate knowledge of these natural features into their traditional practices and cultural understanding of the region.
Collecting rock samples requires special permits from appropriate authorities. The terrain is partly accessible, though proper gear and caution are needed when navigating uneven ground.
The formation preserves fossils of marine organisms that document a shift from deeper ocean conditions to shallow coastal waters. These remains provide rare insight into how marine life adapted to changing environments during this ancient period.
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